What it is: ESR measures the speed of red blood cells moving toward the bottom of a test tube. When inflammation is present, blood proteins stick together and fall and collect more quickly as sediment. The more quickly the blood cells fall, the greater the inflammation.

Why the test is used: ESR is used as a marker of inflammation. Inflammation could indicate lupus activity. This test could be used to monitor inflammation, which could indicate changes in disease activity or response to treatment.

Limitations of the test: Like CRP, the ESR is not specific to lupus. Because there are many causes for a positive result, including infection, the test is not diagnostic for lupus. Nor can it distinguish a lupus flare from an infection. Also, the level doesn't directly correlate with lupus disease activity. So it isn't necessarily useful for monitoring disease activity.

Why the test is used: Abnormalities in blood cell counts, including white blood cells and red blood cells, may occur in people with lupus. This may be related to the lupus, lupus treatments, or infection. For example, leukopenia, a decrease in the number of WBCs, is found in about 50% of people with lupus. Thrombocytopenia, or a low platelet count, occurs in about 50% of people with lupus, as well. Doctors can use this test to monitor these potentially serious problems.

Limitations of the test: Many other medical conditions can cause abnormalities in blood cell counts. So the test by itself is not specific to a lupus diagnosis.

Why the test is used: Abnormalities may indicate the development of complications from lupus. They could also result from treatments for such conditions as kidney disease, elevated blood sugar levels, elevated cholesterol levels, and liver disease.